Facebook employees kick off Hackathon 31 at the Facebook headquarters in Menlo Park, Calif., on Thursday. The Facebook Hackathon, held every few months, is when everyone builds prototypes for new ideas. The Hackathon came a day before Facebook began public trading on Nasdaq.

Facebook employees kick off Hackathon 31 at the Facebook headquarters in Menlo Park, Calif., on Thursday. The Facebook Hackathon, held every few months, is when everyone builds prototypes for new ideas. The Hackathon came a day before Facebook began public trading on Nasdaq. (Francis Luu / Facebook)